1. Field of the Invention
The present invention is related to the area of display devices. More particularly, the present invention is related to Liquid Crystal on Silicon (LCOS) microdevice with color filters so that a corresponding reflective lighting optical system can be simplified.
2. Description of the Related Art
Instead of using liquid crystal between two polarized panels like an LCD (liquid crystal display), an LCOS (Liquid Crystal on Silicon) microdevice has a liquid crystal layer between one transparent thin-film transistor (TFT) and one silicon semiconductor. The semiconductor has a reflective and pixilated surface. The lamp shines light through a polarizing filter and onto the device, and the liquid crystals act like gates or valves, controlling the amount of light that reaches the reflective surface. The more voltage a particular pixel's crystal receives, the more light the crystal allows to pass. It takes several layers of different materials to do this.
In general, LCOS devices have only a very small gap between pixels. The pixel pitch—the horizontal distance between one pixel and the next pixel of the same color—is between 8 and 20 microns (10−6). LCOS technology can produce much higher resolution images than liquid crystal display and plasma display technologies, which makes it less expensive to implement in such devices as televisions.
An LCOS microdevice has a liquid crystal layer between one transparent thin-film transistor (TFT) and one silicon semiconductor. The semiconductor has a reflective, pixilated surface. The lamp shines light through a polarizing filter and onto the device, and the liquid crystals act like gates or valves, controlling the amount of light that reaches the reflective surface. The more voltage the crystal of a particular pixel receives, the more light the crystal allows to pass. It takes several layers of different materials to do this. In general, there are a printed circuit board (PCB) carrying instructions and electricity from the television to the device, a silicon chip controlling the liquid crystal, generally with one transistor per pixel, using data from the television's pixel drivers, a reflective coating reflecting the light to create a picture, a liquid crystal layer controlling the amount of light that reaches and leaves the reflective coating, an alignment layer keeping the liquid crystals properly aligned so they can direct the light accurately, a transparent electrode completing the circuit with the silicon and the liquid crystal, and a glass cover protecting and sealing the entire microdevice.
There are in general two broad categories of LCOS displays: three-panel and single-panel. In three-panel designs, there is one display chip per color, and the images are combined optically. In single-panel designs, one display chip shows the red, green, and blue components in succession with the observer's eyes relied upon to combine the color stream. As each color is presented, a color wheel (or an RGB LED array) illuminates the display with only red, green or blue light. If the frequency of the color fields is lower than about 540 Hz, an effect called color breakup is seen, where false colors are briefly perceived when either the image or the observer's eye is in motion. While less expensive; single-panel projectors require higher-speed display elements to process all three colors during a single frame time, and the need to avoid color breakup makes further demands on the speed of the display technology.
FIG. 1 shows a prior art LCOS system 100 including three LCOS microdevices and an optical engine to form an image from the three LCOS microdevices. A lamp (not shown) produces a beam of white light that passes through a condenser lens. The light is focused and directed to pass through a filter 104 that only allows visible light to pass through, which helps protect the other components. The filtered white light passes through a series of dichroic mirrors 106 that reflect some wavelengths while allowing the rest of the light to pass through. For example, the dichroic mirror 106 can separate red light from the white light, leaving blue and green, and a second mirror can separate the green light, leaving only blue. The newly created beams of colored light simultaneously come into contact with one of three LCOS microdevices 108, 110 and 112—one each for red, green and blue. The reflected lights from the respective microdevices 108, 110 and 102 pass through a prism 114 that combines the lights and creates a full-color image 114. A projection lens 116 is provided and magnifies the image 114 and projects it on the screen 118.
As shown in FIG. 1, the optical engine is mechanically complicated, requiring a lot of manual calibrations to ensure that three reflected images are precisely coincident. If one optical component is off some alignment, a distorted color could be perceived.
There is a need for LCOS microdevices that would require the optical engine less complicated.